The present invention relates to semiconductor devices and, more particularly, to methods of manufacturing a semiconductor device including a contact plug.
A semiconductor device may include constituent elements such as transistors, resistors, capacitors, and metal wires. Contacts in a semiconductor device may transmit electrical signals between these constituent elements.
As the integration density of a semiconductor device increases, design rule may be reduced and high speed operation of the semiconductor device may be desirable. Accordingly, an area of a contact may also be reduced and, as a result, overall resistance of the semiconductor device may be increased.
A contact may generally be formed according to the following method. After forming a contact hole in an interlayer insulating layer to expose a lower structure thereof, a barrier layer having a predetermined thickness may be formed. A metal layer may be deposited on the barrier layer to bury the contact hole. The metal layer and the barrier layer may be etched backed or chemical mechanical polished (CMP) until the interlayer insulating layer is exposed to form a contact plug having a stack layer of the barrier layer and the metal layer barrier layer. A tungsten film may be used for the metal layer in the contact plug.
The barrier layer may be a diffusion prevention layer that may reduce contact resistance with a lower layer thereof and may prevent a reaction between the metal layer and the lower layer in the interlayer insulating layer. The barrier layer may be a Ti/TiN film that has a high step coverage characteristic and may be formed using a chemical vapor deposition (CVD) process. However, since the Ti/TiN film may have a specific resistance much higher than that of the tungsten film, resistance of a semiconductor device may be increased as the integration density of the semiconductor device increases. Also, as the Ti/TiN film formed by CVD process may be formed at a high temperature, other constituent elements may be thermally attacked. Accordingly, the characteristics of the other constituent elements may be degraded.
Recently, studies have been conducted to use a W/WN film formed using an atomic layer deposition (ALD) method as the barrier layer instead of the Ti/TiN film. In the case of the W/WN film formed using ALD, since the resistance characteristic of the contact plug may be improved and the contact plug may be formed at a relatively low temperature (approximately 300° C.), the degradation of the device characteristics of other constituent elements of the semiconductor device may be prevented.
However, in a contact plug structure of W/WN/W, the contact, in particular, may be rapidly etched away from the edge portion thereof since the W in the barrier layer may have a low etch selectivity with respect to a wet chemical material, for example, H2O2 during chemical mechanical polishing a plug having W (hereinafter, referred to as W-plug). The W in the barrier layer may have an etch selectivity of ⅙ of that of the WN in the barrier layer. In some cases, the W-plug may be pulled out from the contact, the occurrence of which is called a pull-out phenomenon. The reason for this may be that since the W-plug may have an area smaller than that of the W in the barrier layer, the W in the barrier layer may be rapidly dissolved along sidewalls of the contact.
FIG. 1 is a plan view scanning electron microscope (SEM) image showing a W-plug pulled-out from a contact. From FIG. 1, it may be observed that a cylindrical W-plug is pulled-out from a contact and contact holes are vacant.
In order to address the above problems, a method of direct-nitridating W has been attempted using plasma when W/WN barrier layer is formed. However, this may cause another problem in that the WN film may be etched due to back bias power during the nitridation plasma process.